Base station apparatus and sequence assigning method

ABSTRACT

Provided is a sequence allocation method capable of reducing inter-cell interference of a reference signal when a ZC sequence is used as the reference signal in a mobile communication system. In the sequence allocation method divides R×M sequences specified by a ZC sequence number r(r=1 to R) and a cyclic shift sequence number m (m=1 to M) into a plurality of sequence groups X (X=1 to R) in accordance with the transmission band width of the reference signal, so that the ZC sequence is allocated to each cell in each sequence group unit. When it is assumed that R=9 and M=6, the number of sequence is 54. Each of the sequence groups is formed by two sequences. Accordingly, the number of sequence groups is 27. The 27 types of sequence groups are allocated to each cell.

TECHNICAL FIELD

The present invention relates to a sequence assignment method in mobilecommunication systems. More particularly, the present invention relatesto a sequence assignment method of assigning a CAZAC (Constant AmplitudeZero Auto-Correlation) sequence to cells in a case of using a CAZACsequence for an uplink reference signal.

BACKGROUND ART

In 3GPP LTE (3rd Generation Partnership Project Long-term Evolution),studies are underway to use a CAZAC sequence such as a Zadoff-Chusequence (hereinafter simply “ZC sequence”) and a generalized chirp-likesequence (hereinafter simply “GCL sequence”) as an uplink referencesignal. A ZC sequence, which has especially good cross-correlationcharacteristics among CAZAC sequences, becomes a focus of attention.

A ZC sequence is represented by the following equation 1. Here, N is thesequence length and r is the sequence number. N and r are coprime.

$\begin{matrix}\lbrack 1\rbrack & \; \\{{c_{r}(k)} = \left\{ {\begin{matrix}{\exp\left( {j\frac{2\pi\; r}{N}\left( {k + \frac{k^{2}}{2}} \right)} \right)} & {{when}\mspace{14mu} N\mspace{14mu}{is}\mspace{14mu}{even}} \\{\exp\left( {j\frac{2\pi\; r}{N}\left( {k + {k\frac{k + 1}{2}}} \right)} \right)} & {{when}\mspace{14mu} N\mspace{14mu}{is}\mspace{14mu}{odd}}\end{matrix},{k = 0},1,\ldots\mspace{11mu},{N - 1}} \right.} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$

With regards to ZC sequence, if the sequence length N is a prime number,N−1 sequences of good cross-correlation characteristics can begenerated. At this time, the cross-correlation between sequences is√{square root over (N)} and fixed. For example, the cross-correlationbetween the ZC sequence of sequence number r=1 and the ZC sequence ofsequence number r=5 that are different sequence numbers, is √{squareroot over (N)} and fixed. On the other hand, if the sequence length N isa number other than prime numbers and if the absolute value of thedifference between two sequence numbers is not coprime to N, the maximumvalue of cross-correlation between these two sequences is greater than√{square root over (N)}.

Further, with regards to a ZC sequence, it is possible to generate, fromone sequence, a plurality of cyclic shift sequences shifted m times theamount of cyclic shift 6 (hereinafter the cyclic shift sequence numberis m.) Then, autocorrelation is ideally zero in all cyclic shiftsequences other than the cyclic shift sequence, which the amount ofshift is zero.

Here, the amount of cyclic shift Δ is designed based on delay spread.This is because, if delay spread exceeds the amount of cyclic shift Δ, adetection error occurs in the base station by detecting a correlationvalue between cyclic shift sequences of different amounts of cyclicshifts within the range of a delay profile detection window set inassociation with m times the amount of cyclic shift Δ.

Further, the transmission time length L of a reference signal is set toa given length, and therefore the number of cyclic shift sequences Mthat can be generated from one ZC sequence is limited, and the followingequation 2 holds.[2]M=L/Δ  (Equation 2)

As a method of assigning a ZC sequence to cells in cases where a ZCsequence having these characteristics is used as a reference signal,studies are conducted for assigning different ZC sequences toneighboring cells and assigning M cyclic shift sequences that can begenerated from one ZC sequence in a cell (see Non-Patent Document 1).FIG. 1 shows this conventional assignment method. Here, ZC sequences ofdifferent sequence numbers (r=1 to 21) are assigned to cells, and cyclicshift sequences (m=1 to 6) are used in each cell. Here, each cellcorresponds to a radio service area. That is, in cases where one basestation provides communication service for a plurality of radio serviceareas, a plurality of cells belong to one base station. When a pluralityof cells belong to one base station, a plurality of cells each may bereferred to as a “sector.” The same applies to the followingexplanation.

In this way, by assigning ZC sequences having low cross-correlations andhaving different sequence numbers to neighboring cells, it is possibleto reduce inter-cell interference. Further, by using cyclic shiftsequences having good autocorrelation characteristics in the same cell,it is possible to reduce interference between mobile stations in thecell and perform accurate channel estimation. The effect of reducinginterference by a plurality of cyclic shift sequences generated from oneZC sequence is greater than by a plurality of cyclic shift sequences ofdifferent sequence numbers.

Non-patent Document 1: R1-062072, MOTOROLA, “Uplink Reference SignalMultiplexing Structures for E-UTRA,” 3GPP TSG RAN WG1 Meeting #46, Aug.28-Sep. 1, 2006

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

Here, the number of ZC sequences is limited, and therefore it isnecessary to reuse a ZC sequence having the same sequence number as a ZCsequence assigned to a cell in different cells. For example, in caseswhere ZC sequences of the same sequence number is assigned to twoneighboring cells, the base station cannot identify which a referencesignal is transmitted from a mobile station in one of cells, andconsequently, an error occurs in the channel estimation result. That is,in cases where ZC sequences of the same sequence number are assigned toa plurality of cells, it is necessary to arrange a plurality of cellsdistant from each other, to prevent inter-cell interference.

On the other hand, the maximum transmission power of a mobile station islimited in uplink, and therefore, when the cell radius is long, toobtain the accuracy of desired channel estimation, it is necessary totransmit a reference signal and data in narrowband (e.g. 360 kHz). Ifthe transmission time length of a reference signal does not change, thesequence length N of a ZC sequence that can be used as a referencesignal is shorter when a transmission bandwidth is narrower.Accordingly, the number of ZC sequences that can be assigned to cellsdecreases. For example, assuming a 360 kHz transmission bandwidth and a30 kHz subcarrier bandwidth, ZC sequence length N is 12 (11 if N is aprime number).

Here, FIG. 2 shows the assignment pattern if the number of ZC sequencesis nine (r=1 to 9). If the number of ZC sequences is small like this, ZCsequences that can be assigned to cells decreases, and therefore ZCsequences of the same sequence number have to be assigned to a pluralityof relatively nearby cells. As a result, interfering a reference signalincreases between the nearby cells.

It is therefore an object of the present invention to provide a sequenceassignment method that can reduce inter-cell interference of referencesignals in mobile communication systems.

Means for Solving the Problem

The present invention where a Zadoff-Chu sequence is used as a referencesignal includes: grouping R×M sequences specified by Zadoff-Chu sequencenumbers r (r=1 to R) and the cyclic shift sequence numbers m (m=1 to M)into a plurality of sequence groups according to transmission bandwidthsfor reference signals; and assigning a plurality of sequences belongingto a same group to one cell.

Advantageous Effect of the Invention

According to the present invention, ZC sequences are grouped into aplurality of sequence groups according to transmission bandwidth forreference signals, so that it is possible to increase the number ofsequence groups by reducing the number of sequences included in asequence groups. Consequently, even in cases where reference signals aretransmitted in narrow bands, it is possible to determine a sequencegroup assigned to a cell from a large number of sequence groups andreduce interference between different cells.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a conventional ZC sequence assignment method;

FIG. 2 shows a conventional assignment pattern;

FIG. 3 shows the virtual sequence groups (in cases where the numberaccording to transmission bandwidths is six), according to Embodiment 1;

FIG. 4 shows the virtual sequence groups (in cases where the numberaccording to transmission bandwidths is two), according to Embodiment 1;

FIG. 5 shows the assignment method according to Embodiment 1;

FIG. 6 shows a block diagram showing the configuration of the basestation according to Embodiment 1;

FIG. 7 shows a block diagram showing the configuration of the mobilestation according to Embodiment 1;

FIG. 8 shows the assignment method according to Embodiment 2;

FIG. 9 shows the assignment pattern according to Embodiment 2;

FIG. 10 illustrates cross-correlation characteristics of a ZC sequenceaccording to Embodiment 2;

FIG. 11 shows the assignment method according to Embodiment 3; and

FIG. 12 shows the assignment method according to Embodiment 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, embodiments of the present invention will be described in detailwith reference to the accompanying drawings.

Embodiment 1

In the sequence assignment method according to Embodiment 1 of thepresent invention, in a case of using ZC sequences for uplink referencesignals, R×M sequences specified by the ZC sequence numbers r (r=1 to R)and the cyclic shift sequence numbers m (m=1 to M) are grouped into aplurality of sequence groups as a unit of predetermined number accordingto transmission bandwidths for reference signals, and ZC sequences areassigned to each cell in the sequence group units. For example, when R×Mis twenty and when ten sequence groups are generated, the predeterminednumber is two. Further, when R×M is sixty and when ten sequence groupsare generated, the predetermined number is six.

In the following explanation, R×M sequences specified by the ZC sequencenumbers r (r=1 to R) and the cyclic shift sequence numbers m (m=1 to M)are referred to as “virtual sequences” and are specified by virtualsequence number Z. Further, a group formed with these virtual sequencesis referred to as a “virtual sequence group” and is specified by virtualsequence group number X.

FIG. 3 (where the predetermined number is six) and FIG. 4 (where thepredetermined number is two) show the relationships between the virtualsequence group numbers (X), the ZC sequence numbers r, the cyclic shiftsequence numbers m and the virtual sequence numbers Z where thepredetermined numbers according to transmission bandwidths for referencesignals are six or two, in tables, respectively. A virtual sequencegroup refers to the group formed with a plurality of different virtualsequences. A virtual sequence group may be formed with virtual sequencesof different ZC sequence numbers, but it is preferable to be formed withvirtual sequences of the same ZC sequence number from a viewpoint toreduce interference. In the table in FIG. 3, similar to a conventionalmethod, one virtual sequence group is associated with one ZC sequencenumber, and R is the number of virtual sequence groups in cases where ZCsequence numbers can be used up to R. Meanwhile, in the table in FIG. 4,three virtual sequence groups are associated with one ZC sequencenumber, so that the number of virtual sequence groups is 3R, and it islearned that the number of virtual sequence groups increases. Forexample, in cases where transmission bandwidths for reference signalsare narrow, it is possible to use the setting of FIG. 4 where the numberof virtual sequences is reduced for a narrow band. In other cases, it ispossible to use the setting of FIG. 3.

Further, in the table in FIG. 3, one virtual sequence group isassociated with one ZC sequence number and cyclic shift sequence numbers1 to 6. However, one virtual sequence group may be associated with aplurality of ZC sequence numbers and cyclic shift sequence numbers 1 to6 of each ZC sequence number. That is, virtual sequence group 1 may beassociated with cyclic shift sequence numbers 1 to 6 of ZC sequencenumber 1 and cyclic shift sequence numbers 1 to 6 of ZC sequence number2. For example, in cases where transmission bandwidths for referencesignals are narrower than a threshold value, the table in FIG. 3 may beused, and, meanwhile, in cases where transmission bandwidths forreference signals are wider than a threshold value, the number ofvirtual sequences included in one virtual sequence group may increase.In cases where transmission bandwidths for reference signals are wide,the number of virtual sequences is large, so that it is possible tomaintain the distance between base stations reusing the same sequence tobe a distance of little interference between sequences, even when thenumber of virtual sequences included in one virtual sequence group isincreased. Further, in virtual sequence groups, the number of sequencesthe mobile stations can use increases, so that, by the effect ofrandomizing the sequence numbers, it is possible to reduce interferencewithin a virtual sequence group or reduce interference between virtualsequence groups.

FIG. 5 shows the method of assigning the virtual sequence groups (thenumber of virtual sequences: 2) in FIG. 4, to cells. Here, assuming R=9and M=6, the number of virtual sequences is fifty four kinds. Meanwhile,each virtual sequence group is formed with two virtual sequences, andthe number of virtual sequence groups is twenty seven kinds. In theassignment method according to the present embodiment, these twentyseven kinds of virtual sequence groups are assigned to cells. In aconventional assignment method, nine kinds need to be assigned to cells.

Now, an example of methods of determining the number of virtualsequences included in each virtual sequence group will be explained.

In uplink data transmission, the minimum unit of transmission bandwidthis determined, and the mobile station transmits data using the minimumunit of bandwidth or a plurality of minimum units bandwidths.

Consequently, when the transmission bandwidth for reference signals iswide, there may be a large number of mobile stations transmitting datain the bandwidth. At this time, it is necessary to multiplex referencesignals in the same transmission bandwidth for channel estimation of themobile stations. For example, in cases where a transmission band forreference signals are 1.25 MHz, if the minimum transmission bandwidthfor data transmission is 375 kHz, reference signals of three mobilestations need to be multiplexed. The example here presumes that allmobile stations transmitting data transmit reference signals. However,assuming that two kinds of virtual sequences included in a virtualsequence group are assigned, it is difficult to multiplex referencesignals from three mobile stations in the same transmission bandwidth.Consequently, in cases where transmission bandwidth is wide, it isnecessary to set the larger number of virtual sequences assigned to onecell.

On the other hand, when the transmission bandwidth for reference signalsis narrow, it is less likely to be a large number of mobile stationstransmitting data in the bandwidth, and therefore it is less likely tohave to multiplex a large number of reference signals. If thetransmission band for reference signals is 375 kHz, a reference signalof one mobile station alone may be transmitted. In this way, the numberof virtual sequences required to be assigned to one cell variesdepending on a transmission bandwidth for reference signals and theminimum transmission bandwidth of data. Then, the virtual sequences aregrouped into a plurality of virtual sequence groups according totransmission bandwidths.

As explained above, when the transmission bandwidth for referencesignals is narrow, it is possible to reduce the number of virtualsequences included in a virtual sequence group and increase the numberof virtual sequence groups.

Increasing and decreasing the number of virtual sequence groups bychanging the predetermined number is very preferable in view of the factthat the number of cyclic shift sequences varies according to thesequence length N. For example, in a conventional assignment method, thedistance between base stations reusing the same sequence is longer whenthe band is broader, and inter-cell interference decreases between thesame sequences. However, if the bandwidth exceeds a certain extent, thedistance between base stations is long enough, so that inter-cellinterference between the same sequences little occurs, and theinter-cell interference between the same sequences little decreases evenif the bandwidth is wider.

On the other hand, in the assignment method according to the presentembodiment, the number of virtual sequences assigned to one cell is setto the necessary predetermined number according to the bandwidths, sothat lower flexibility in assignment due to decrease of the number of ZCsequences can be compensated for, thereby enabling assignment withsuppressed interference. For example, by increasing the number ofvirtual sequences included in one virtual sequence group in broadband,the number of virtual sequences the mobile stations can use increasesand the mobile stations can change virtual sequences used in a giveninterval, so that, by the effect of randomizing sequences, it ispossible to reduce interference in a virtual sequence group or betweenvirtual sequence groups. Further, it is possible to reduceinter-sequence interference between a virtual sequence group of a widebandwidth and virtual sequence group of a narrow bandwidth. The distancebetween base stations reusing the same sequences can be maintained inmore than a given distant, so that it is possible to suppress inter-cellinterference low because of the same sequence.

Next, FIG. 6 shows base station 100 according to the present embodiment.

In base station 100, transmission data and control information areencoded in encoding section 110, modulated in modulating section 111,subjected to transmission processing including D/A conversion,amplification and up-conversion in RF transmitting section 112 andtransmitted to mobile stations from antenna 101.

RF receiving section 102 performs receiving processing includingdown-conversion and A/D conversion on signals received from mobilestations via antenna 101, and outputs the signals to separating section103.

Separating section 103 separates a signal received as input to areference signal, a data signal and a control signal, and outputs thedata signal and the control signal to equalizing section 104 and thereference signal to channel estimating section 107.

Equalizing section 104 equalizes the data signal and the control signalusing channel fluctuation estimated in channel estimation section 107,and outputs the signals after equalization processing to demodulatingsection 105.

Demodulating section 105 demodulates the data signal and control signal,and outputs the signals to decoding section 106.

Decoding section 106 decodes the signal received as input afterdemodulation, to acquire received data.

Channel estimation section 107 measures uplink channel characteristicsfrom the reference signal received as input using the ZC sequence numberand cyclic shift sequence number associated with the virtual sequencegroup number of the cell belonging to base station 100 (“local cell”),and outputs the measurement result to scheduling section 108 andequalizing section 104.

Scheduling section 108 performs scheduling based on the measurementresult received as input. Further, scheduling section 108 assigns the ZCsequence number and cyclic shift sequence number associated with thevirtual sequence group number of the local cell to the reference signalof each mobile station.

Control information generating section 109 generates control informationusing the above assignment method.

Next, FIG. 7 shows the configuration of mobile station 200 according tothe present embodiment.

Mobile station 200 has: determining section 205 for determining the ZCsequence number and cyclic shift sequence number assigned to the mobilestation based on the control information transmitted from base station100; and reference signal generating section 206 for generating areference signal according to the ZC sequence number and cyclic shiftsequence number assigned to the mobile station.

RF receiving section 202 performs receiving processing includingdown-conversion and A/D conversion on the signal received from basestation 100 via antenna 201, and outputs the signal to demodulatingsection 203.

Demodulating section 203 demodulates the signal received as input fromRF receiving section, and outputs the demodulated signal to decodingsection 204.

Decoding section 204 decodes the signal after demodulation, to acquiredata signal and control information. The control information related tothe reference signal is outputted to determining section 205.

Determining section 205 determines the ZC sequence number and cyclicshift sequence number assigned to the mobile station, and outputs thedetermination result to reference signal generating section 206.

Reference signal generating section 206 generates a reference signalbased on the ZC sequence number and cyclic shift sequence numberinputted from determining section 205, and outputs the reference signalto multiplexing section 209.

On the other hand, transmission data is encoded in encoding section 207and modulated in modulating section 208, and outputted to multiplexingsection 209.

Multiplexing section 209 time-multiplexes transmission data andreference signal received as input, and outputs the time-multiplexedsignal to RF transmitting section 210.

RF transmitting section 210 performs transmission processing includingD/A conversion, amplification and up-conversion on the reference signaland data symbol, and transmits the reference signal and data symbolafter transmission processing to base station 100 from antenna 201.

In this way, according to the present embodiment, by setting the numberof virtual sequences included in a virtual sequence group according totransmission bandwidths for reference signals, it is possible toincrease the number of virtual sequence groups upon narrowbandtransmission. For this reason, even when a reference signal istransmitted in a narrowband, a virtual sequence group assigned to a cellcan be determined from a large number of virtual sequence groups, sothat it is possible to reduce inter-cell interference with referencesignals. Further, in a broadband, by increasing the number of virtualsequences included in one virtual sequence group, it is possible toreduce inter-cell interference with the reference signals by therandomization effect.

Embodiment 2

In the present embodiment, in cases where virtual sequence groups aregrouped such that each virtual sequence group is formed with virtualsequences of the same ZC sequence number as shown in the table in FIG.4, virtual sequence groups of the same ZC sequence are preferentiallyassigned to cells belonging to the same base station. That is, in a caseof using the table in FIG. 4, virtual sequence groups (X), that is,X1=3k, X2=3k+1 and X3=3k+2, are preferentially assigned to cellsbelonging to one base station. In this way, the common ZC sequencenumber is preferentially used in a plurality of cells belonging to thesame base station, and different cyclic shift sequences are used betweencells in the same base station. FIG. 8 shows the method of assigningthis virtual sequence group (the number of virtual sequences: 2) tocells. Referring to FIG. 8, the ZC sequences of the same sequence numberr (e.g. r=1) are used in the cells belonging to the same base station(e.g. three cells in a shaded part in FIG. 8). Then, in the cells of thesame base station different cyclic shift sequences m are used. That is,m=1, 2 are used in cell #1, m=3, 4 are used in cell #2, m=5 and 6 areused in cell #3.

Next, FIG. 9 shows assignment patterns to cells in the assignment methodaccording to the present embodiment. The number of ZC sequences is nine.As apparent from this assignment method compared to the conventionalassignment method shown in FIG. 2, according to the present embodiment,the distance between a plurality of base stations using the same ZCsequence can be longer than in a conventional case. Consequently, it ispossible to decrease inter-cell interference between different basestations using the same ZC sequence.

Further, it is possible to reduce interference between cells belongingto the same base station. If sequence length N is a prime number, themaximum value of correlation between different sequences is √{squareroot over (N)} and fixed. On the other hand, if the sequences are thesame, the maximum value of correlation is N. FIG. 10 shows thecorrelation characteristics between sequences of these ZC sequences (inthe case of r=2). At this time, the difference between a correlationvalue between different ZC sequences and a correlation value between thesame ZC sequences decreases when the sequence length N is shorter.Consequently, in a conventional method, even when ZC sequences ofdifferent sequence numbers are used between neighboring cells, effect ofsuppressing inter-cell interference with reference signals decreaseswhen the sequence length N is shorter. By contrast with this, accordingto the present embodiment, in the cells that establish frame timingsynchronization and that belong to the same base station, delay spreadis determined so as not to exceed the amount of cyclic shift Δ, so thatit is possible to reduce interference by using cyclic shift sequencesorthogonal to each other at the interval Δ, and consequently, it ispossible to reduce interference between cells belonging to the same basestation.

Although establishing synchronization with frame timings (i.e. uplinkand downlink transmission or reception timing) between cells belongingto different base stations is difficult, establishing synchronizationwith frame timings between cells belonging to the same base station isrelatively easy. For the reason, it is relatively easy to performmultiplexing by cyclic shift sequences between cells belonging to thesame base station.

Further, in a communication system where synchronization with frametimings is established between cells belonging to different basestations (i.e. synchronization system between base stations), the cellswhere a virtual sequence group of the same ZC sequence is preferentiallyassigned is not limited to the cells belonging to the same base station,and may be neighboring cells. Even if this sequence assignment isperformed, it is possible to reduce inter-cell interference withreceived signals.

Embodiment 3

In the present embodiment, in cases where the number of virtualsequences included in a virtual sequence group of Embodiment 2decreases, the cyclic shift sequence numbers m to be assigned to cellsare discontinuous numbers. That is, assignment is given to cells at aninterval of cyclic shift sequence numbers m.

FIG. 11 shows an example of the assignment method according toEmbodiment 3. In FIG. 11, cyclic shift sequence numbers m=1, 4 areassigned in cell #1, m=2, 5 are assigned in cell #2, m=3 and 6 areassigned in cell #3. Although, in FIG. 11, the same ZC sequence numberis used in three cells belonging to the same base station, the presentembodiment is not limited to this.

In this way, according to the present embodiment, each virtual sequencegroup is formed with virtual sequences, which are virtual sequences ofthe same ZC sequence number and which are virtual sequences ofdiscontinuous numbers. Accordingly, it is possible to reduceinterference by the delay wave exceeding the amount of cyclic shifttransmitted from the same cell. When the reference signal of cyclicshift sequence number m=2 is the delayed wave exceeding the amount ofcyclic shift A, in the base station, the reference signal is detected inerror as cyclic shift sequence number m=1. Further, this error detectioninterferes with cyclic shift sequence number m=1. However, according tothe present embodiment, for example, only the ZC sequences of cyclicshift sequence numbers m=2, 5 are used in one cell, so that, even whenthese ZC sequences are received as ZC sequences of cyclic shift sequencenumber m=1 in the base station, the reference signal is not detected inerror. That is, according to the present embodiment, it is possible toreduce interference between reference signals in one cell.

Embodiment 4

In the present embodiment, in cases where the number of virtualsequences included in a virtual sequence group of Embodiment 2decreases, cyclic shift sequence numbers are reused between cellsbelonging to the same base station. That is, in the cells belonging tothe same base station, different cyclic shift numbers are used betweenneighboring cells, and cyclic shift sequence numbers are reused betweencells that are not neighboring each other.

FIG. 12 shows an example of assignment method according to Embodiment 4.In FIG. 12, it is assumed that there are six cells belonging to the samebase station, and the same ZC sequence is used in the cells (e.g. thesix cells in shaded parts in FIG. 12). In the example shown in FIG. 12,cyclic shift sequence numbers m are reused between cells in the samebase station, like m=1, 2 in cells #1 and #4, m=3, 4 in cells #2 and #5,m=5, 6 in cell #3 and #6.

Consequently, according to the present embodiment, cyclic shift sequencenumbers are reused between cells in the same base station, so that, evenwhen the number of cells increases, it is possible to make longer thedistance between base stations using the same sequence number and reduceinter-cell interference. The same cyclic shift sequence numbers m arenot used in neighboring cells, so that influence of inter-cellinterference between cells is little.

The embodiments of the present invention have been explained.

In all the embodiments explained above, it is possible to reduce theamount of report signaling. For example, assuming that cyclic shiftsequence numbers m=1 to 6, six kinds (m=1 to 6) of the cyclic shiftsequences are used in a conventional case. However, in the presentinvention, two kinds of the cyclic shift sequences are used (forexample, m=1, 2 in cell #1, m=3, 4 in cell #2, and m=5, 6 in cell #3).

For this reason, in a conventional method, the base station selects acyclic shift sequence number from six kinds (m=1 to 6) and reports it tothe mobile stations. That is, as a report of cyclic shift sequencenumber to mobile stations, it is necessary to provide three bits foreach mobile station.

By contrast with this, in the present invention, the base station mayselect a cyclic shift sequence number from two kinds and report it tothe mobile stations. The cyclic shift sequence numbers are limited totwo kinds, for example, cyclic shift sequence numbers 1 and 2 in cell#1, cyclic shift sequence numbers 3, 4 in cell #2, cyclic shift sequencenumbers 5, 6 in cell #3. That is, when the present invention isimplemented, as a report of cyclic shift sequence number for each mobilestation, one bit may be provided for each mobile station.

Meanwhile, the mobile station estimates a cyclic shift sequence numberassigned to the cell where the mobile station belongs, from one-bitreport information transmitted from the base station. For example, whenone-bit report information (for example, 1) is reported, the mobilestation located in cell #1 (cyclic shift sequence m=1, 2) can determinem=1, the mobile station located in cell #2 (cyclic shift sequence m=3,4) can determine m=3, and the mobile station located in cell #3 (cyclicshift sequence m=5, 6) can determine m=5. In this way, according to thepresent invention, it is possible to reduce the amount of reportsignaling.

Further, although the present invention is especially effective in caseswhere transmission bandwidth for a reference signal is narrow, thepresent invention is not limited to this.

Further, the predetermined number may be changed such that the number ofvirtual sequence groups are the same between transmission bandwidths forreference signals. That is, when twenty virtual sequence groups aregenerated in each transmission bandwidth, the predetermined number maybe set according to the number of the groups.

Further, it is effective that the base station and the mobile stationshare information of virtual sequence groups and virtual sequencenumbers. For example, the base station and the mobile station may sharea table showing the relationships between virtual sequence groups andvirtual sequence numbers.

Further, all numbers in virtual sequence numbers may not be included ina virtual sequence group. That is, there may be virtual sequence numbersunused.

Further, in the above explanation, cells in the same base station havebeen explained as an example. However, they may also be the cells whereframe synchronization is established.

Further, the present invention may be applied to a part of transmissionbandwidth instead of all transmission bandwidth.

Further, although cases have been explained above where the number ofvirtual sequences included in a virtual sequence group is two kinds, thepresent invention is not limited to this.

Further, cases have been explained above presuming that each virtualsequence group is assigned to a cell. However, it may be presumed thateach virtual sequence group is assigned to a base station. For example,virtual sequence group 1 of FIG. 3 may be assigned to the base station,and the base station may allocate virtual sequence numbers 1 to 6included in virtual sequence group 1 to the cells or mobile stations.

Further, generally, the sequence length is longer when transmissionbandwidths are wider, and therefore, setting the number of virtualsequences included in a virtual sequence group according to thetransmission bandwidths for reference signals equals setting the numberof virtual sequences included in a virtual sequence group according tothe sequence length of a reference signal.

Further, although cases have been explained using ZC sequences, thepresent invention may be applied to CAZAC sequences, ZC sequences witheven lengths, GCL sequences, Frank sequences, PN sequences such as Msequences and gold sequences, sequences that CAZAC sequences aretruncated or extended, sequences that CAZAC sequences are punctured,Random CAZAC sequences, OLZC sequences, RAZAC sequences and othersequences generated by a computer.

Further, a base station in the above embodiments may be referred to as“Node-B,” and a mobile station may be referred to as “UE.”

Moreover, although with the above embodiment a case has been describedwhere the present invention is configured by hardware, the presentinvention may be implemented by software.

Each function block employed in the explanation of the aforementionedembodiment may typically be implemented as an LSI constituted by anintegrated circuit. These may be individual chips or partially ortotally contained on a single chip. “LSI” is adopted here but this mayalso be referred to as “IC,” “system LSI,” “super LSI” or “ultra LSI”depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells within an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosure of Japanese Patent Application No. 2006-271051, filed onOct. 2, 2006, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is applicable to, for example, mobilecommunication systems.

The invention claimed is:
 1. A base station apparatus comprising: atransmitter configured to transmit, to a mobile station, controlinformation related to a sequence in one of multiple groups, into whichsequences for each of multiple sequence lengths having at least twodifferent lengths are divided; and a receiver configured to receive areference signal, which is generated using the sequence in one of themultiple groups based on the control information and which istransmitted from the mobile station, wherein each of the multiple groupscontains a respective predefined number of sequence(s), and eachrespective predefined number depends on one of the sequence lengths, andwherein a first respective predefined number of sequence(s) contained ina first group of the multiple groups into which sequences having a firstsequence length are divided is less than a second respective predefinednumber of sequences contained in a second group of the multiple groupsinto which sequences having a second sequence length are divided wherethe first sequence length is less than a threshold value and the secondsequence length is greater than or equal to the threshold value.
 2. Thebase station apparatus according to claim 1, wherein the respectivepredefined number of sequence(s) contained in each of the multiplegroups varies depending on the sequence lengths.
 3. The base stationapparatus according to claim 1, wherein the control informationidentifies the sequence in one of the multiple groups.
 4. The basestation apparatus according to claim 1, wherein the control informationidentifies one of the multiple groups.
 5. The base station apparatusaccording to claim 1, wherein the reference signal has one of at leasttwo different lengths.
 6. The base station apparatus according to claim1, wherein the sequences for one sequence length of the reference signalare divided into the multiple groups.
 7. The base station apparatusaccording to claim 1, wherein each of the multiple groups contains thesame number of the sequence(s).
 8. The base station apparatus accordingto claim 1, wherein one of the multiple groups is assigned to the mobilestation depending on a cell.
 9. The base station apparatus according toclaim 1, wherein the sequence is a Zadoff-Chu sequence.
 10. The basestation apparatus according to claim 1, wherein the sequences includemultiple cyclically shifted sequences derived from a sequence throughdifferent cyclic shift values.
 11. The base station apparatus accordingto claim 1, wherein the sequences for each sequence length are dividedinto a number of the multiple groups, and the number is constantregardless of the sequence length.
 12. A sequence assigning methodcomprising: transmitting, to a mobile station, control informationrelated to a sequence in one of multiple groups, into which sequencesfor each of multiple sequence lengths having at least two differentlengths are divided; and receiving a reference signal, which isgenerated using the sequence in one of the multiple groups based on thecontrol information and which is transmitted from the mobile station,wherein each of the multiple groups contains a respective predefinednumber of sequence(s), and each respective predefined number depends onone of the sequence lengths, and wherein a first respective predefinednumber of sequence(s) contained in a first group of the multiple groupsinto which sequences having a first sequence length are divided is lessthan a second respective predefined number of sequence(s) contained in asecond group of the multiple groups into which sequences having a secondsequence length are divided where the first sequence length is less thana threshold value and the second sequence length is greater than orequal to the threshold value.
 13. The method according to claim 12,wherein the respective predefined number of sequence(s) contained ineach of the multiple groups varies depending on the sequence lengths.14. The method according to claim 12, wherein the control informationidentifies the sequence in one of the multiple groups.
 15. The methodaccording to claim 12, wherein the control information identifies one ofthe multiple groups.
 16. The method according to claim 12, wherein thereference signal has one of at least two different lengths.
 17. Themethod according to claim 12, wherein the sequences for one sequencelength of the reference signal are divided into the multiple groups. 18.The method according to claim 12, wherein each of the multiple groupscontains the same number of the sequence(s).
 19. The method according toclaim 12, wherein one of the multiple groups is assigned to the mobilestation depending on a cell.
 20. The method according to claim 12,wherein the sequence is a Zadoff-Chu sequence.
 21. The method accordingto claim 12, wherein the sequences include multiple cyclically shiftedsequences derived from a sequence through different cyclic shift values.22. The method according to claim 12, wherein the sequences for eachsequence length are divided into a number of the multiple groups, andthe number is constant regardless of the sequence length.